Sulphuric acid is used for many different industrial purposes. One application of sulphuric acid is for the treatment of raw biomass, such as wood or grass, so that in a subsequent step it may be subjected to hydrolysis, to set free the hydrocarbons, in particular carbohydrates (sugars) such as hexose and pentose, which then may be converted to useful products, e.g. in a fermentation step.
Cellulose makes up the major part of all plant biomass. The source of all cellulose is the structural tissue of plants. It occurs in close association with hemicellulose and lignin, which together comprise the major components of plant fiber cells. This complex of cellulose, hemicellulose and lignin is usually referred to as lignocellulose. Cellulose consists of long chains of beta glucosidic residues linked through the 1,4 positions. These linkages cause the cellulose to have a high crystallinity and thus a low accessibility to enzymes or acid catalysts. Hemicellulose is an amorphous hetero-polymer which is easily hydrolyzed. Lignin, an aromatic three-dimensional polymer, is interspersed among the cellulose and hemicellulose within the plant fiber cell.
Although there are alternatives for effecting the release and hydrolysis of lignocellulose, such as enzymatic processes and processes employing extrusion or steam explosion, such processes are generally expensive.